The effect of acid and alkali unfolding and subsequent refolding on the pro-oxidative activity of trout hemoglobin

The pro-oxidative activity of trout hemoglobin was significantly increased at low pH (2.5-3.5) in a washed fish muscle (WFM) system. It was found that the more unfolded the hemoglobin was the more exposed its heme group was, which increased its pro-oxidative activity. The amount of oxidation products produced (TBARS) were, however, lower at low pH vs neutral pH. At pH 10.5-11, the pro-oxidative activity of hemoglobin was greatly suppressed. The conformation of hemoglobin was significantly more stable at high pH as compared to pH 7 as judged by its visible absorption spectrum. Hemoglobin readjusted from low pH to pH 7 had a higher pro-oxidative activity (i.e., more rapid oxidation) in WFM than native hemoglobin at pH 7, even though TBARS values were lower than in the untreated sample at pH 7. The results suggest that the WFM becomes slightly more susceptible to oxidation after low pH treatment but also produces less TBARS. The increased pro-oxidative activity after pH readjustment correlated well with an incomplete recovery in the native structure on pH readjustment. A longer unfolding time and a lower pH led to a less refolded hemoglobin with increased pro-oxidative activity. Hemoglobin was less pro-oxidative at low pH in the presence of 500 mM NaCl. The presence of salt did, however, increase the pro-oxidative properties of hemoglobin after readjustment to pH 7. The treatment of washed fish muscle at alkaline pH followed by adjustment to pH 7 led to a slight delay in hemoglobin-mediated lipid oxidation in WFM as compared to native hemoglobin at pH 7. The results suggest that WFM becomes less susceptible toward oxidation after pH readjustment from alkaline pH. These results clearly show that for muscle protein extraction/isolation processes requiring highly alkaline or acidic conditions, alkaline conditions are preferred if the lipid oxidation originating from hemoglobin is to be minimized.     

Changes in foliar elements in red spruce seedlings after exposure to sulfuric and nitric acid mist

Red spruce (Picea rubens Sarg.) seedlings were exposed repeatedly at a field site or in a greenhouse to acidic mist containing the major sulfur and nitrogen pollutants of wet deposition in the eastern U.S.: sulfate alone, nitrate alone or with ammonium ion, and a combination of these ions. Acidities and ion concentrations ranged from below the mean to above the maximum concentration for cloudwater in the eastern U.S. Effects on elements in current-year foliage were examined after continuous or intermittent overnight exposures to mist performed over periods of 6 to 19 weeks. Principal findings from five experiments conducted over a three-year period were that acidic mist 1) increased the foliar S and/or N content when exposures were intermittent with repeated opportunities for drying of liquid on foliage; 2) decreased foliar calcium, and/or magnesium content, especially when exposures to acidic mist were continuous rather than intermittent; and 3) gave inconsistent results for foliar iron and aluminum probably because of deposition of soil particles and contamination with metals from the mist delivery system. These results indicate that long-duration exposures to cloudwater with pH below 3 may alter foliar nutrient composition and change relationships between N, S, Ca, and Mg, with potential consequences for growth and resistance to natural stress factors.     

Modelling pH buffering and aluminium solubility in European forest soils

The pH buffering and aluminium solubility characteristics of acid soil are important in determining the soil's response to changes in precipitation acidity. The chemistry of soil organic matter (humic substances) plays a key role in both processes, yet is complex and still poorly understood. Nevertheless, models of humic substance chemistry have been developed, one of which is WHAM–S, which contains a model (Model V) of proton and metal binding at discrete sites on humic substances and considers electrostatic effects on the binding strength. Here we have tested the ability of WHAM–S to model solution pH and Al using batch titration studies on organic and mineral soil horizons from forested sites in Norway, Germany and Spain, with ambient pH values from 3.73 to 5.73. We optimized the model predictions by adjusting the amounts of soil aluminium and humic substances within defined limits, taking the contents of copper chloride‐extractable Al and the base‐extractable organic matter as starting values. The model simulated both pH and dissolved Al well with optimized amounts of aluminium and humic substances within the defined limits (root mean squared error for pH from 0.01 to 0.22, for p[Al]_aq (total dissolved Al) from 0.03 to 0.49, five data points). Control of dissolved Al by dissolved organic matter was important particularly at above‐ambient pH. In two mineral horizons we improved the fits by assuming that Al could precipitate as Al(OH)₃. The optimized model also gave reasonable predictions of pH and dissolved Al in supernatants obtained by repeated leaching of the soil horizons. The results show that humic substances dominate the control of pH and dissolved Al in most of the horizons studied. Control by Al(OH)₃ occurs but is the exception.     

Effect of soil pH on cation and anion solubility

Abstract

The effect of soil pH on the exchangeability and solubility of soil cations (Ca, Mg, Na, K, and NH₄‐N) and anions (NO₃‐N, Cl, and P) was investigated for 80 soils, spanning a wide range in physical and chemical properties and taxonomic groups. This information is needed from environmental and agronomic standpoints to estimate the effect of changes in soil pH on leachability and plant availability of soil nutrients. Soils were incubated with varying amounts of acid (H₂SO₄) and base (CaCO₃) for up to 30 days. Although acid and base amendments had no consistent effect on cation exchangeability (as determined by neutral NH₄OAc), amounts of water‐soluble Ca, Mg, Na, K, NH₄‐N, and P decreased, while NO₃‐N and Cl increased with an increase in soil pH. The increase in cation solubility was attributed to an increase in the negative charge of the soil surface associated with the base addition. The change in surface electrostatic potential had the opposite effect on amounts of NO₃‐N and Cl in solution, with increases in N mineralization with increasing soil pH also contributing to the greater amount of NO₃‐N in solution. The decrease in P solubility was attributed to changes in the solubility of Fe‐, A1‐, and Ca‐P complexes. The logarithm of the amount of water‐soluble cation or anion was a linear function of soil pH. The slope of this relationship was closely related (R² = = 0.90 ‐ 0.96) to clay content, initial soil pH, and size of the cation or anion pool maintaining solution concentration. Although the degree in soil pH buffering increased with length of incubation, no effect of time on the relationship between cation or anion solubility and pH was observed except for NO₃‐N, due to N mineralization. A change in soil pH brought about by acid rain, fertilizer, and lime inputs, thus, affects cation and anion solubility. The impact of these changes on cation and anion leachability and plant availability may be assessed using the regression equations developed.     

Changes in soil pH due to the storage of soils

Abstract. The pH of soil samples was remeasured after storage for 20 years in the laboratory. The pH decreases were minor in acid to neutral soils (-0.3), but greater in alkaline soils (-0.63). The pH differences were statistically significant only for alkaline soils. The decreases of pH with time are probably mainly due to the decomposition of organic matter, the CO₂ produced, the hydroscopic water and the presence of CaCO₃.     

Changes in Rainwater pH associated with Increasing Atmospheric Carbon Dioxide after the Industrial Revolution

Water, Air, & Soil Pollution - This paper examines the historical change in the pH of natural rainwater due to increased atmospheric CO2 from 1800 until 2007, giving predicted change in 2100....     

Field and laboratory studies of exposures of brown trout to acid waters

Some recent work on the effects of acid waters on brown trout are presented. Laboratory bioassay experiments have demonstrated that yearling trout are relatively insensitive to pH >4.3. Aluminium is demonstrated to be extremely toxic with suppression of growth occurring at concentrations above 20 μg L^?1 at pH 4.4 to 5.2. Aluminium toxicity is reduced at high pH (5.9 and 6.3). Field studies carried out on 61 acidic and circumneutral streams in upland areas of England and Wales showed a strong relationship between water quality and standing crop of 1+ brown trout. Measured pH levels per se were too high to be directly toxic. On the other hand, heavy metal and Al concentrations could account for low or zero brown trout biomass in the more acidic streams. A mobile bioassay laboratory has been developed to allow controlled bioassay experiments to be carried out in the field. Natural and synthesised waters can be tested concurrently in multi-factorial experiments with in situ determinations of pH, Ca, Al (total and monomeric) and other water quality characteristics.     

Aluminium sulphate solubility in acid forest soils in Denmark

Ion leaching in 3 sandy spruce forest soils of different origin and pH was investigated in the laboratory. Zero-tension lysimeters containing undisturbed soil columns of varying soil depth were subjected to H₂SO₄ loadings for a period of 9 weeks. The analysis of the resulting leachate supports the hypothesis that Al-sulphate minerals may form in acidic soils when exposed to acid (H₂SO₄) deposition. In the B horizon of a glaciofluvial sandy soil (pH 4.2), both H⁺ and sulphate ions were retained to maintain 2pH + PSO₄ = 11.9 in the leachate solutions. This relation between H⁺ and sulphate activity may be due to an adsorption mechanism or a precipitation mechanism. The precipitation mechanism is favored by the good fit of leachate composition to the conditions for jurbanite [AlOHSO₄] formation from gibbsite [Al(OH)₃]. In the B horizon of a sandy till at pH 3.7, the Al in soil solution (0.5 mmol L^?1) was leached with sulphate. As the sulphate load was increased, some sulphate was retained. This may also be due to the dissolution and precipitation of an Al-sulphate mineral. The ion activity products of leachate solutions from the B horizon of this soil were close to the pK_s reported for jurbanite. The conditions for the possible existence and/or formation of Al-sulphate minerals in acidic soils are discussed.     

Changes in conformation and subunit assembly of cod myosin at low and high pH and after subsequent refolding

Conformational and structural changes of cod myosin at pH 2.5 and 11 and after subsequent pH readjustment to pH 7.5 were studied. Results suggest that on acid unfolding, the myosin rod may fully dissociate due to electrostatic repulsion within the coiled coil, while it does not dissociate at alkaline pH. Both pHs led to significant conformational changes in the globular head fraction of the myosin heavy chains, suggesting that it takes on a molten globular configuration. A large part of the myosin light chains are lost on both pH treatments. On pH readjustment to neutrality, the heavy chains take on a structural form similar to the native state with the coiled-coil rod reassociating from acid pH while leaving the globular head less packed, more hydrophobic and structurally less stable. The irreversible change brought about in the globular head region leads to the failure of light chains to reassemble onto it, a drastic loss in ATPase activity, and more exposure of reactive thiol groups. The acid and alkali processes therefore lead to substantial changes in the globular part of the myosin molecule and perhaps more importantly to different molecular changes in myosin, depending on which pH treatment is employed.     

Response of Ammophila breviligulata to acid rain and low soil pH

The effects of simulated acid rain and low soil pH on the growth of Ammophila breviligulata (Cape Strain), American beach grass, were studied in greenhouse experiments. Plants treated with acid rain were shorter, but shoot density, live shoot biomass, and rhizome biomass were not adversely affected by the acid rain treatments. Root biomass was greatest in the acid rain treatments. A manipulated soil pH of 4.0, typical of that found in field sites of dying beach grass, resulted in significantly reduced plant height, shoot density, shoot biomass, and rhizome biomass. Root biomass was greater in the low pH treatment and was six times greater than rhizome biomass in that treatment while the root to rhizome ratio was approximately 1∶1 in the control — likely a reflection of the plant's response to decreased nutrient availability in the low pH soil. Acid rain treatment of dune sand resulted in the leaching of Al, a potentially phytotoxic element.     

Pro-oxidative characteristics of trout hemoglobin and myoglobin: a role for released heme in oxidation of lipids

The molecular mass of trout myoglobin was 16017 Da based on electrospray ionization mass spectrometry. A Root effect (low oxygen affinity at pH 6.3) was determined in trout hemoglobin but not myoglobin. At pH 6.3, myoglobin autoxidized more rapidly (3.5-fold) as compared to anodic hemoglobin. Anodic hemoglobin was a better catalyst of lipid oxidation in washed cod muscle as compared to myoglobin at pH 6.3. This suggested that some process other than met heme protein formation was the rate-limiting step in lipid oxidation processes. Heme loss rates were determined using the apomyoglobin mutant H64Y prepared from sperm whale. Anodic hemoglobin released its heme group much more rapidly than myoglobin. In comparisons of anodic and cathodic hemoglobins, heme loss rate better predicted the onset of lipid oxidation than autoxidation rate. These studies collectively suggest that heme dissociation has a primary role in the ability of different heme proteins to promote lipid oxidation processes.     

Reduction in soybean yield after exposure to ozone and sulfur dioxide using a linear gradient exposure technique

A linear gradient field exposure system was modified from one originally described by Shinn et al. (1977) and used to expose field grown soybeans (Glycine max cv Hark) to a concentration gradient of a mixture of two gaseous pollutants: SO₂ and 0₃. Since this technique does not use enclosures, study plants experienced near ambient fluctuations in environmental conditions, including wind, and hence were exposed to widely fluctuating pollutant concentrations. Plants in the gradient system were exposed to both pollutants for 57 h on 12 days during the pod-filling period (31 August–17 September). Mean concentrations during the 57 h of exposure at the ‘high’ end of the gradient were 0.16 and 0.06 µl l^?1 (PPM) SO₂ and O₃, respectively, with 10 h at greater than 0.25 and 0.10 µl^?1 SO₂ and O₃, respectively. Total doses for these plants were estimated to be 9.0 and 3.5 µl^?1 · h SO₂ and O₃, respectively. Comparison with plants exposed to ambient air indicated that exposure to SO₂ and O₃ reduced total yield per plant and dry mass per bean by as much as 36 and 15 %, respectively. Since concurrent exposure to a much higher dosage of SO₂ alone (20.2 µl l^?1 · h) was observed in a separate experiment to have no significant effect on yield, 03, although present at moderately low levels, was probably responsible (alone or synergistically with SO₂) for the greatest reduction in seed size and yield.     

Effects of pH and heat treatments on the structure and solubility of potato proteins in different preparations

The soluble potato proteins are mainly composed of patatin and protease inhibitors. Using DSC and both far-UV and near-UV CD spectroscopy, it was shown that potato proteins unfold between 55 and 75 degrees C. Increasing the ionic strength from 15 to 200 mM generally caused an increase in denaturation temperature. It was concluded that either the dimeric protein patatin unfolds in its monomeric state or its monomers are loosely associated and unfold independently. Thermal unfolding of the protease inhibitors was correlated with a decrease in protease inhibitor activities and resulted in an ionic strength dependent loss of protein solubility. Potato proteins were soluble at neutral and strongly acidic pH values. The tertiary structure of patatin was irreversibly altered by precipitation at pH 5. At mildly acidic pH the overall potato protein solubility was dependent on ionic strength and the presence of unfolded patatin.     

Aluminium solubility mechanisms in moderately acid Bs horizons of podzolized soils

The processes controlling the retention and release of aluminium in acid forest soils are still subject to controversy, and therefore a universal hypothesis as to what mechanisms are operating has not been firmly established. By studying the Bs horizons of Swedish and Swiss podzolized soils, and by analysing data in the literature, we have found that aluminium hydroxide, and in some cases also poorly ordered imogolite, may control Al solubility in moderately acid (pH > 4.2–4.3) Bs horizons. The strongest evidence in support of the presence of a quickly reacting Al(OH)₃ pool came from the temperature dependence of Al solubility in a Bs horizon, which was consistent with the reaction enthalpy of an Al(OH)₃ phase such as gibbsite, and from the observation that the ion activity product for Al(OH)₃ was the same regardless of whether equilibrium was reached from over‐ or undersaturation. The pool of Al(OH)₃ is commonly small and may be completely dissolved after large additions of acid. This may be explained by the continuing redissolution of reactive Al(OH)₃ to form less soluble imogolite‐type phases. By using the same methods it was found that soil suspensions did not reach equilibrium with poorly ordered imogolite even after 17 days. Thus, imogolite probably does not control Al solubility in the short term in many soils despite the common occurrence of this mineral. This is due to the relatively slow kinetics of imogolite formation and dissolution, especially at low temperatures and at small solution H₄SiO₄ concentrations.     

Boreal forest microbial community after long-term field exposure to acid and metal pollution and its potential remediation by using wood ash

A 2²-factorial design with sulphuric acid (pH 3.1) and Cu-Ni addition was used to assess the effects of moderate amounts of continuous acid (Acid and CuNi+Acid) and metal (CuNi and CuNi+Acid) deposition on humus microbial activity and community structure in the field after nine growing seasons. These 20 field experiment samples were also used to measure the suitability of wood ash for remediation. Microcosms were treated with wood ash at a fertilization rate of 5000 kg ha⁻¹, irrigated with water and incubated for 2 months in the dark at 20 °C and a constant relative humidity of 60%. Microcosms only irrigated with water served as a control. Microbial activity was measured as basal respiration. Microbial community structure was determined by phospholipid fatty acid analysis, which mainly targets bacteria. Fungal community structure was assessed by 18S rDNA-targeted polymerase chain reaction-denaturing gradient gel electrophoresis analysis. The bioavailability of Cu was tested with the Pseudomonas fluorescens DF57-Cu15 reporter strain, which bioluminescences in the presence of Cu. Our field study showed, that acid and metal treatments both changed the humus layer microbial community structure. Acid application decreased humus layer pH and base saturation (BS) and increased the amounts of both extractable and bioavailable Cu. Metal application increased the concentration of extractable Ni and changed the fungal community structure. In irrigated laboratory microcosms the above-mentioned treatment effects were still seen except for the acid and metal effects on microbial and fungal community structures. For ash-treated microcosms, neither acid nor metal effects were found for humus layer pH, BS, extractable Cu and Ni, or bioavailable Cu. Thus, wood ash can be used for remediation of acid and metal polluted humus.     

Behavior of manganese in some acid soils in Western Germany in relation to pH and air-drying

The relationships of pH to Mn concentrations in equilibrium soil solutions of strongly acid soils (pH < 4.5) were studied. The values of Mn concentrations did not conform to the solubility relationships of MnO₂, Mn₂O₃ or Mn(OH)₃. On the othr hand, a significant relationship between pMn and exchangeable Mn (r = 0.636^**, N =43) was observed. This suggest that the levels of Mn in solution are primarily controlled by exchangeable Mn in response to pH changes.

Mineral soil samples when air-dried showed a 1.5 to more than 8-fold increase in amounts of NH₄Cl-extractable Mn. This increase was not observed in soil samples rich in organic matter (> 5% organic carbon), thus excluding the possibility of release of Mn from the organic fraction of the soil. The increase is considered a consequence of increased solubility of Mn-oxides.     

Changes in soil solution composition and pH in urine-affected areas of pasture

Changes in soil solution composition and concentrations of exchangeable cations and mineral N in undisturbed cores of pasture soil were investigated in two experiments following applications of sheep urine to the cores. The major cations applied in the urine were K⁺ and Na⁺, and the major anions were HCO₃^? and Cl^?. Addition of urine increased concentrations of exchangeable K⁺, Na⁺ and NH₄⁺ and measured ionic strength of the soil solution throughout the surface 15 cm of soil, demonstrating that the urine moved through the core by macropore flow immediately following addition. Immediately following urine application the ionic strength in soil solution in the surface 2.5 cm of soil increased from 4–6 MM to 24–41 mM. Hydrolysis of urine-urea was extremely rapid, and in less than 1 d high concentrations of NH₄⁺-N (i.e. 270–370 mg N kg^?1) had accumulated in the surface 0–2.5 cm of the urine patch, and soil pH had risen by over one unit. Nitrification then proceeded and, after approximately 15 d, NO₃^? became the dominant form of mineral N present. During nitrification, soil pH declined and the ionic strength of the soil solution increased substantially with NO₃^? becoming the dominant anion present in solution. There were concomitant increases in the concentrations of Ca²⁺ and, to a lesser extent, Mg²⁺ in the soil solution as NO₃^? concentrations increased. After approximately 30 d, concentrations of exchangeable NO₃^? had risen to 250–330 mg N kg^?1, soil solution NO₃^? concentrations had increased to about 80 mmol, dm^?3, and ionic strength in the soil solution had increased to 130–140 mM. These results demonstrate the dominating effect of N transformations in causing large fluctuations in the pH, ionic composition and ionic strength of the soil solution in the urine patch. It was concluded that nutrient availability in the patch was affected directly by nutrient addition in urine, and also probably indirectly through the fluctuations in soil solution pH and ionic strength that occur.     

Changes in amino acid and organic acid composition in tomato and cucumber plants in relation to salinity and nitrogen nutrition

Under conditions of salt stress, plants show qualitative and quantitative alterations in various organic compounds, such as nitrogen (N) compounds and organic acids. In this work, the effect of different saline levels as well as various N levels, supplied as nitrate (NO₃) or as ammonium (NH₄)+NO₃ on the concentration of amino acids and organic acids in the leaves of tomato and cucumber plants has been studied. The effect of the source of N on individual amino acid contents varied with plant species. Most of the amino acids increased when the concentration of N in the nutrient solution was increased, except when N was added as NH₄+NO₃ for tomato. The effect of salt stress depended on which amino acid was considered. The data also indicate that the effect of salinity on each particular amino acid was greatly dependent on the plant species and N source. Organic acids were differently affected by salinity and by the N source, depending on the plant species. In tomato, the concentrations of short‐chain organic acids were 2–3 times higher in NO₃‐supplied plants than in those grown with NH₄+NO₃. Finally, in cucumber, malic acid concentration increased as a function of the saline level in the medium.